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2. Hormone concentrations in plasma (Expt 1 only) were determined by radioimmunoassay. Rates of [U-14C]-acetate and D-[U-14C]glucose incorporation and oxidation by subcutaneous and abdominal adipose tissue removed at slaughter, together with rate of glycerol release, were determined during in vitro incubation in all three experiments.

4. Feeding of lotus high in CT was associated with a consistent but non-significant increase in the rate of glycerol release from adipose tissue, which was reduced as dietary reactive CT concentration was lowered through PEG application, and a reduction in the lipogenesis: lipolysis value. Selection for leanness decreased acetate incorporation and increased glycerol release from adipose tissue, with the effect not interacting with the diet.

1. Diets of fresh kale (Brassica oleracea) and ryegrass (Loliumperenne) – elover (Trifolium repens) herbage were fed to growing sheep in three experiments. In Expts 1 and 3 the sheep were confined indoors and fed at hourly intervals, and all were given supplementary iodine to counteract kale goitrogens. Lambs grazed the two forages for 24 weeks in Expt 2, with and without intramuscular injections of iodized oil. The kale and herbage contained respectively 11 and <0.1 g S-methyl-L-cysteine sulphoxide (SMCO)/kg dry matter (DM) and values for readily fermentable: structural carbohydrate (CHO) were 3.1 and 0.8, respectively.

2. Blood samples were withdrawn from indwelling catheters (Expts 1 and 3) or venipuncture (Expt 2) and the plasma analysed for a range of hormones using radioimmunoassay procedures. Glucose irreversible loss (GIL) was measured in Expt 1 using primed continuous infusions of D-[U-14C]glucose. Samples of adipose tissue were removed from the shoulder area in Expt 3, and rates of D-[U-14C]glucose and [U-14C]acetate incoporation and oxidation were measured in vitro, together with the rate of glycerol release.

3. In the presence of supplementary I2, kale feeding was associated with an elevation in plasma concentration of free thyroxine (T4) Regardless of I2 supplementation, sheep fed on kale had much higher plasma growth hormone concentrations than sheep fed on ryegrass-clover herbage, and this was accompanied by reduced plasma somatostatin concentrations.

4. Plasma insulin and glucagon concentrations were similar for sheep fed on the two diets; GIL tended to be slightly but not significantly greater (9.4%) for sheep fed on kale than for those fed on ryegrass-clover herbage.

5. Kale feeding was associated with increased uptakes of acetate and glucose into adipose tissue, reduced rates of oxidation of both substrates and no difference in rate of glycerol release. Each 1 nmol increase in glucose uptake was associated with 8.7 nmol acetate uptake ( P < 0.001).

6. It is proposed that ruminants counteract protein inactivation, caused by production of dimethyl disulphide from SMCO in the rumen, through increasing circulating concentrations of growth hormone and T4, which then stimulate synthesis of replacement body proteins.

Two experiments are reported in which mature, castrated male sheep were used to study the effect of a change of magnesium status, as induced by a continuous intravenous infusion of magnesium, on the faecal output of magnesium. In the first experiment, three artificial diets differing markedly in fibre content but extremely low in magnesium were used and in the second experiment, natural diets of frozen grass and of hay and ground barley.

With the artificial diets, unit change in plasma magnesium concentration gave the same increase in faecal magnesium output with all three diets but on average faecal magnesium output was highest for the diet containing the highest content of fibre and least for the diet containing an intermediate amount of fibre, and the differences, though small, were statistically significant. With the natural diets, there was no significant difference between diets in the increase in faecal magnesium output in response to a change of plasma magnesium concentration but the order of response was much greater than for the artificial diets. It is concluded that absorption of magnesium from the gut is depressed at high plasma magnesium concentrations.

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